Centrifugally controlled coning lock for bladed rotors



April 24, 1951 M. D. BUIVID 2,549,887

7 CENTRIFUGALLY CONTROLLED CONING LOCK FOR BLADED ROTORS Filed April 21, '1949 '5 Sheets-Sheet 1 MICH-EL o. BUIVID INVENTOR ATTORNEY M. D. BUIVID April 24, 1951 CENTRIFUGALLY CONTROLLED CONING LOCK FOR BLADED ROTORS 5 Sheets-Sheet 2 Filed April 21, 1949 MICHEL D. BUIVID INVENTOR BY [.7 /awu ATTORNEY M. D. BUIVID April 24, 1951 C ENTRI FUGALLY CONTROLLED CONING LOCK FOR BLADED ROTORS S Sheets-Sheet 4 Filed April 21, 1949 MICHEL D. BUIVID INVENTOR hz/RM ATTORNEY April 24, 1951 M. D. BUlVlD 2,549,887

CENTRIFUGALLY CONTROLLED comm; LOCK FOR BLADED ROTORS Filed'April 21, 1949 5 Sheets-Sheet 5 MICHEL D. BUlVlD INVENTOR ATTORNEY Patented Apr. 24, 1951 'CENTRIFUGALLY CONTROLLED CONING LOOK. FOR BLADE!) ROTORS Michel D. Buivid, Milford, Conn, assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application April 21, 1949, Serial No. 88,748

6 Claims. 1

This invention relates to helicopters and more particularly to improved means for inhibiting flapping of rotor blades for certain speeds of the rotors thereof. When helicopters of the type having freely hinged blades are slowed down and brought to rest, gusts of wind can act upon the blades to cause them to flap. If the wind velocity is high such flapping may damage the blades or other parts of the aircraft. This problem is even more pronounced during operation on or from aircraft carriers where the wind velocity over th flight deck is usually high" and gust conditions are prevalent. Therefore, it is necessary to provide an anti-flapping device to restrain the blades and prevent their being damaged. However, when the helicopter is in flight the flapping of the blades must be unrestrained to prevent undesirable actions'resulting from gyroscopic and transverse moments (caused by the difference in air speed of advancing and retreating blades), gusts of wind and the like.

Therefore it is an object of this invention to provide an improved rotor blade stop for looking the blade against flapping either upwardly or downwardly when the rotor is slowed down to a predetermined velocity or is standing still.

Another object of this invention is to provide positive locking means for restraining the blade against flapping upwardly when the speed of the rotor falls below a predetermined value while utilizing a fixed bumper stop for preventing blade droop.

A still further object of this invention is to provide in one of its embodiments a hydraulically controlled locking mechanism which positively restrains the rotor blade from flapping upwardly or downwardly below the predetermined speed of the rotor including mechanism for permitting theblade to slowly assume a substantially horizontal position in the event that the centrifugally operated controls happen to restrain the flapping movement when the blade is still in a position above the normal horizontal position.

These and other objects will become readily apparent from the following detailed description of the accompanying drawings.

In these drawings,

Fig. 1 is a side view of a helicopter incorporating this invention.

' Fig. 2 is a front elevation of a portion of a helicopter rotor head including a blade flapping link and its corresponding locking mechanism shown in partial'cross section.

Fig. 3 is a front elevation of a portion of a V ient bumper 34.

er bolts it.

- 2 rotor head indicating a hydraulic type blade flapping lock.

Fig; 4 is a partial top View of the rotor head taken along the line 4--4 of Fig. 3 indicating the blade configuration in the vicinity of the flapping hinge.

Fig. 5 is a top view of the rotor head of Fig. 3 indicating the operative positions of the flight weights for the centrifugal control.

Fig. 6 is a perspective view of a helicopter rotor head showing another form of the hydraulically controlled type of locking mechamsm.

Fig. '7 is a front elevation showing a portion of the mechanism of Fig. 6 including a partial cross section of the hydraulic unit.

In Fig. 1 a helicopter ID has rotor blades l2 and I4 which upon rotating support the helicopter ll) in the-air'and in so doing may flap upwardly to the dotted line positions shown. Means for providing a droop stop and for looking the blades in their normal horizontal posi-' tion against upward flapping movement are provided at [6' and are constructed and arranged to lock the blades in the position shown in solid lines when the rotor blades are turning slowly, for example, below R.P.M., and are adapted to yield and permit the blades to fiap upwardly when the speed of rotation of the rotor exceeds 100 R;P.M.

Referring to Fig. 2 which represents a purely mechanical form of this invention, the helicopter drive shaft 2t carries adjacent its upperend a flap hinge 22 and a flapping link 24, which at its outboard end is attached to the blade l2 by means of a drag link 26. The drive shaft 2i has fixed thereto a collar 36 and a substantially horizontal plate member 32 which carries a resil- The collar 38, plate 32 and the bumper 34, being fixed to the drive shaft 20, rotate in unison therewith so that the bumper 34 is always in position to be engaged by the flapping link 2d thereby forming a droop stop for the blade E2. The outboard extremities of the plate member 32 are reinforced against flexing by a plurality of tubular struts 40 which are fixed at their lower ends to the collar 30 by means of welded gussets l2 and are connected at their upper ends to the plate 32 by means of a housing 35 which is connected to the plate 32 by means The housing 45 carries a slidable latch 5% which is biased in an outboard direction by a sp-ring' 'EZ. "A flyweight arm lit including ball weight 62 is pivotally attached at 63 to a bracket 64 carried by the housing 46. The upper end of the arm 60 carries a cam 66 which engages the latch 56 on an internal surface 68 thereof whereby the latch will be moved inboard against the bias of the spring 52 when the ball weight 62 moves outwardly to the dotted line position under increased rotational speed of the rotor. In the position shown in Fig. 2 the latch 56 is in its extended position whereby it can engage the collar 12 which is slidably carried by an extension 14 of the drag link pin. A spring I8 normally biases the collar I2 into its uppermost position on the extension I4 and serves to absorb any jarring shocks which might result when the latch 60 and the collar I2 engage.

Thus it is apparent that in the position shown in Fig. 2 the blade I2 including its flapping link 24 is prevented from drooping by means of the bumper 34 and will be prevented from flapping upwardly since the collar I2 will become engaged with the latch 56. It should be noted that the collar 22 may be positioned by the spring I8 if desired so that the collar 72 is in juxtaposition with the latch 56 and no gap exists between these engaging members. When the speed of the rotor is increased to an amount where the centrifugal force acting on the weight 62 overcomes the bias of the spring 52 the latch member 59 will be moved inboard thereby permitting the blade I2 to flap freely upward.

The lock of this invention may take the form of a hydraulically operated mechanism as shown in Fig. 3. Herein the drive shaft 26 has fixed thereto a pair of transverse plate members 90 between the outer extremities of which a blade I2 is attached by means of a flapping hinge 92. A resilient bumper SM is fixed between the plate members 90 wherein it can abut a recessed surface 96 on the blade hinge connection to prevent the blade from drooping beyond a substantially horizontal position.

To prevent the blade from flapping upwardly a plunger type latch 98 is provided whereby the latch may engage the recessed surface 96 at a point above the flapping hinge axis. The plunger $8 is slidably mounted within a housing I60 fixedly carried between the plates 90 and is biased in an outboard direction by a spring I132. The plunger 98 has a chamber ID I into which hydraulic fluid may be admitted via the flexible conduit I66 from the hydraulic reservoir I08; the reservoir being vented to the atmosphere (not shown) to prevent either positive or negative pressures from being built up therein. The flow of hydraulic fluid between the reservoir and the chamber I64 in the latch 98 is controlled by a rotatable valve H2 which can close off the flow of fluid from the reservoir to the conduit I66 and the chamber I64. To this end the valve I I2 carries a collar I I4 which is fixed thereto by means of a pin I I6 and carries a torsional biasing spring II8 for maintaining the valve H2 in the closed position. The spring I I8 is capable of producing its torsional bias inasmuch as one end thereof is fixed to the collar I I4 and the other end thereof is fixed to the reservoir housing.

The upper end of the valve H2 is fixed to the flyweight arm I22 so that when the speed of the rotor is increased beyond a predetermined value the flyweight arm I22 moves toward the radial dotted position shown in Fig. thereby rotating the valve H2 against the bias of spring HR to the open position shown in Fig. 3 whereby fluid is free to return from the chamber I04 back to the reservoir I08. Under these conditions the blade will be free to flap upwardly thereby forcing the plunger 98 inwardly and forcing fluid back into the reservoir.

As the rotor slows down below a predetermined speed and the blade Ill approaches the horizontal position shown in Fig. 3 the spring I02 will tend to force the latch 98 outwardly While at the same time the fiyweight arm I22 will return from the dotted to the full-line position shown in Fig. 5 thereby permitting the spring M8 to rotate the valve I I2 to a closed position. Under these conditions fluid will be trapped in the conduit I06 and the chamber I04 so that the latch 98 will remain in the extended position to prevent upward flapping of the blade I4 (Fig. 1).

It may be desirable to control two or more blades in thi same manner by providing a plurality of hydraulic connections from the reservoir I68 to the latch mechanisms of each of such blades.

Fig. 6 indicates a preferred embodiment of this invention and generally indicates a helicopter rotor hub (with only one blade shown for the sake of clarity) including a blade root I26 and the usual pitch control mechanism IZI. The drive shaft I2 5 carries a flapping hinge I26 including a flapping link I28 which carrie at its outboard extremity a drag link I 36. Means for damping the movements of the blade about the drag link I36 may be provided. However, for convenience,

the damper mechanism has been omitted from this figure. A triangular bracket I66 is fixed to the drive shaft I22 by means of mounting straps I42 and at its outer extremity carries a droop stop bumper I4 5 which prevents the flapping link I28 and the rotor blade from flapping downwardly beyond a predetermined substantially horizontal position. In order to restrain the blade from flapping upwardly at rotational speeds of the rotor below a predetermined value, a hydraulic locking mechanism I5!) is provided comprising a cylinder I52 which is pivotally mounted at its upper end at I54 to a pair of brackets I56 which are fixed to the triangular bracket I40. A piston rod I66 which cooperates with the cylinder I52 is pivotzlly connected to the flapping link I28 a 6 As better seen in Fig. 7 the cylinder I52 includes a piston I6 3 slidable therein and a passage I66 which permits fluid communication from one side of the piston to the other side thereof. A flyweight assembly H6 is provided for controlling a valve H2 which opens and closes the passage I66 to either permit free fluid communication between the opposite sides of the piston I64 or to close oif such communication. A fluid reservoir I86 is provided whereby fluid may pass via the flexible conduit I82 into the passage I66 to compensate for the unequal volumes of the chambers formed on either side of the piston I64 within the cylinder I52.

At relatively low rotational speeds of the rotor the fiyweight assembly IlIl will assume the dotted line position shown in Fig. 7 thereby rotating the valve I72 to a closed position and trapping hydraulic fluid above the piston I64 to positively lock the piston and the flapping link I26 connected thereto against upward flapping movement. Conversely when the flyweight assembly III] assumes the full-line position shown in Fig. 7, i. e., during rotational speeds above a predetermined value, the valve I22 will be in the open position as shown to permit free fluid communication between the opposite sides of the piston I64 thereby unlocking the system and permitting free upward flapping of the link I 28 and its associated blade I20.

In the event that the blade happens to be in a flapping position above the normal substantially horizontal position when the valve 172 is closed at relatively low rotational speeds, a means is provided to permit the blade to slowly descend to the normal position wherein it will remain locked while preventin any further upward movement thereof. To this end a bleed passage I90 and a ball check valve 92 in the piston [64 permits fluid to pass from the bottom of the cylinder through the piston and thence to the top side of the cylinder I52. Since the check valve I92 permits the fluid to flow only upwardly it will be apparent that the blade ME? and the flapping link I28 can settle downwardly toward its neutral position but subsequent upward movement will be prevented, assuming of course that thevalve I72 remains in a closed position.

As the result of this invention it is apparent that an improved blade flapping lock has been provided whereby the blades of the helicopter can be positively restrained against upward and downward flappin when the rotor speeds are below a predetermined value.

Further as a result of this invention a simple but rugged lock mechanism has been provided wherein a minimum of repair and preventive maintenance is necessary.

Although certain preferred embodiments of this invention have been illustrated and de-- scribed herein, it will be apparent that various changes and modifications can be made in the form and arrangements of the various parts without departing from the scope of this novel concept.

What it is desired by Letters Patents is:

1. In a helicopter rotor having a hub and blade, pivot means for connectin said blade and hub providing upward and downward flapping movement of said blade, resilient bumper means carried by said hub for limiting the downward movement of said blade, a cylinder carried by said hub, piston means reciprocable in said cylinder and having an operative connection with said blade for limiting the upward movement of said blade, a source of hydraulic fluid having a fluid line operatively connected to said cylinder, and means responsive to the speed of said rotor including a valve for controlling the flow of fluid in said fluid line and controlling the position of said piston means.

2. In a helicopter rotor having a rotatable hub and a blade pivoted to said hub for upward and downward movements relative thereto, bumper means carried by said hub and engageable by said blade for limiting the downward movement of said blade, a cylinder carried by said hub, a piston reciprocable in said cylinder having an operative connection with said blade for limiting the upward movement of said blade, a source of fluid including a fluid line operatively connected with said cylinder and means responsive to the speed of rotation of said hub below a predetermined value for releasably locking said piston in said blade limiting position including a rotary valve for trapping fluid in said cylinder.

3. In a helicopter rotor having a rotatable hub and a blade pivoted to said hub for upward and downward movements relative thereto, means fixed to said hub for limiting the downward movement. of said blade below a normal substantially horizontal position, cooperating hydraulic means carried respectively by said hub and blade for limiting the upward movements of said blade including relatively movable and stationary elements, hydraulic control means carried by one of said elements for restricting the relative movement between said elements, and means responsive to an increase in speed of said rotor above a predetermined value for disabling said restrictive control means.

4. In a helicopter rotor having a rotatable hub and a blade pivoted to said hub for upward and downward movements relative thereto, means carried by said hub for limiting the downward movement of said blade below a substantially horizontal position, hydraulic means for limiting the upward movements of said blade including cooperating piston and cylinder elements one of which is connected to said blade and the other to said hub, means establishing fluid communication between one side of said piston and the other side thereof whereby fluid is permitted to flow therethrough upon relative movement of said piston and cylinder elements, valve means for restricting said fluid flow, and means responsive to a predetermined speed of said hub for opening said valve means.

5. In a helicopter rotor having a. rotatable hub and a blade pivoted to said hub for upward and downward flapping movements relative thereto, abutment means for limiting downward movement of said blade, means for limitin upward movement of said blade including a hydraulic cylinder pivotally supported by said hub and a cooperating piston pivotally supported by said blade, said cylinder and piston forming variable volume chambers, means enabling said blade to move upwardly including passage means establishing fluid communication between said chambers, valve means in said passage means for restricting the latter, and mechanism operative in response to rotor speeds below a predetermined value for operating said valve in a closing direction and limiting the upward movement of said blade.

6. A device according to claim 5 wherein said mean limiting the upward movement of said blade includes bleed means for permitting a slow downward movement of said blade toward said abutment means including a unidirectional valve operative when said passag means is restricted by said valve means and said blade is above said abutment means.

MICHEL D. BU IVID.

nnrnnencns or an The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,980,169 Cierva Nov. 13, 1934 2,475,333 Morris July 5, 1949 OTHER REFERENCES Ser. No. 254,867, Flettner (A. P. 0.), published May 25, 1943. 

